In a gasifier which generates combustible gas by pyrolyzing a biomass fuel such as coal and woody pellets or carbonaceous feedstock such as pet cork, ashes of the carbonaceous feedstock is melted and is accumulated in a slag hopper, which is provided in a bottom portion of the gasifier, as slag. Slag water (cooling water) is stored in the slag hopper, and the slag falls into the slag water, is rapidly cooled to be solidified and crushed.
In this way, the slag which is solidified, crushed, and stored in the slag hopper is discharged out of a system of the gasifier via a lock hopper which is provided outside the gasifier. Since the slag has a higher density than the slag water, in the related art, when the slag is moved from the slag hopper to the lock hopper, the slag falls naturally by gravity. For example, PTL 1 discloses a slag discharge system in which a lock hopper is disposed on a lower portion of a gasifier.
However, according to the above-described slag discharge system, a installation position of the gasifier is high in order to provide the lock hopper on a lower portion of the gasifier. Accordingly, a height from an installation surface of a plant to the upper of the gasifier increases. If the installation position of the gasifier becomes high, a installation position of a supporting frame for supporting the gasifier, an operating frame, or the like becomes high.
Accordingly, a slag discharge system disclosed in PTL 2 is suggested. In the slag discharge system, a lock hopper is disposed on a side of a gasifier, a slag discharge line communicating from a slag hopper to a lock hopper is provided, a water flow from the slag hopper to the lock hopper is formed in the slag discharge line by a circulation pump, and slag in the slag hopper is discharged to the lock hopper by the water flow.
Accordingly, since the slag can be transferred from the slag hopper to the lock hopper according to the flow of the slag water, the lock hopper can be disposed on the side of the gasifier, and a height from an installation surface of a plant to the upper portion of the gasifier can be suppressed to a low level.